Mine did the same thing this morning on my way into work. Last time I held down the volume button for 20 seconds and it reset, but this time it stayed off my whole trip to the office. Hopefully it will come back on it's own after work for my ride home. I had not yet gotten the 4.1 upgrade so I am worried that this was caused by a failed upgrade.

 

Mine was fine the next time I started the vehicle. I find if I have an issue I lock and set the alarm and come back a little later and all is well again.

Of course one of those times was the start of a 5 hour drive, which is a little awkward to pull into a gas station at the very start of the trip with the family and dog and then lock and set the alarm and maybe put two gallons of gas in as a delay tactic so I can restart the car and pray it all works again.

I find the Spotify app the most infuriating. No rhyme or reason for why sometimes its not available even when leaving or driving in the exact same geographic area over and over. I'm assuming that's a JLR server issue if anything.